1. Field of the Invention
The present invention relates to electrical systems for jet aircraft, and more particularly to a modular electrical harness assembly for use on the main landing gear of a jet aircraft.
2. Description of the Background Art
The aviation industry is generally divided into two major providers, major air carriers and regional air carriers. The major carriers are those who operate larger jet aircraft that are capable of transporting passengers over greater distances. These aircraft are routinely used both in intercontinental and trans-oceanic operations. The second provider, the regional carrier, provides point to point service on shorter routes and feeder service to their major air carrier partners according to the hub and spoke method. This service is accomplished through the use of smaller turbo propeller and fan jet aircraft, normally ranging in size between 45 and 90 passengers.
With the increased demand on air carriers to provide more point to point and better on time service, the regional carriers have flourished through partnerships with major air carriers. Major carriers usually sign long term contracts with regional partners on a fee per departure basis which guarantees the regional operator a fixed price every time the aircraft leaves the gate, whether it is full of passengers or not.
The major carriers typically handle all of the reservation services and advertising, with the regional carriers aircraft painted to look like those of their major carrier partners. The only responsibility the regional carrier has is to make sure that the aircraft leaves the gate on time. For this their cost for operating the aircraft are covered and they are given an agreed upon profit margin. The major carrier is responsible for filling the seats. Accordingly, it has become ever more important to make sure that the aircraft operated by the regional carrier is able to depart on time when scheduled in an airworthy manner, because when it is unable to perform, the regional carrier looses money.
One of the major problems causing certain regional jet operators to miss and/or cancel flights was electrical failures in the landing gear anti-skid system. The landing gear anti-skid system includes an electrical harness which is mounted on the main landing gear of the aircraft. There are four harnesses of this type per aircraft and they monitor and control the anti-skid system along with the brake temperature monitoring system and the weight off wheels system.
Electrical harnesses send signals about different aircraft functions and parameters to the aircraft flight control deck for monitoring by computers and the aircrafts crew. A failure in the harness sends false signals which can cause erroneous readings and interpretations. These false readings and interpretations can cause flights to be cancelled and lengthy troubleshooting efforts to identify and repair the problem.
Extensive research found that a landing gear anti-skid harness had several flaws that contributed to the failures and/or to the lengthy troubleshooting and repair efforts. The first problem with a harness was that it had no feature to prevent the contamination of a harness by dirt and/or liquids. The second, and more important problem, was that when troubleshooting a harness, because of its design nature, it was impossible to remove and replace a single portion of a harness, without disrupting the entire harness. This usually meant that the aircraft would have to be removed from the gate and returned to the hangar for extensive troubleshooting and maintenance. Flights were cancelled and revenue was lost when this problem occurred.
Once back at the hangar, the work of troubleshooting and repairing a harness had just begun. Once the problem with a harness was found, which usually was attributed to a failure of the anti-skid portion due to moisture ingress, the entire harness would have to be replaced. This procedure called for the complete aircraft to be lifted into the air via jacks and then the harness in question to be removed in its entirety. This process would normally take a skilled crew between four and six hours to accomplish.
Once a harness had been removed a complete new harness would have to be reinstalled and the landing gear would have to be retracted and extended several times along with other functional tests in order to calibrate the new harness and confirm all systems were operational. Since the complete harness assembly would have to be removed and replaced, additional harness assemblies would have to be maintained in stock, at different locations, which would add additional inventory and cost burden to the carrier.
In total, an aircraft needing to have one harness replaced in this manner would usually be removed from service and at the hangar for at least eight to ten hours. This would mean that its total usage for that day would have to be cancelled and if another aircraft was not put into service to cover its original flight cancellation, then additional flights within the system would be adversely effected. This would cause loss revenue and customer dissatisfaction which could have catastrophic consequences in the long term.
In addition, is has been found that certain portions of prior art harnesses were burdened with significant limitations. More particularly, it has been found that prior art harnesses, and particularly the upper main sub-assembly failed after, and mostly as a result of, repeated retraction and extension of the landing gear. Failure of the main sub-assembly may result in exposure and/or damage of the internal wires.
Accordingly, there is a need for a harness that is more reliable and user friendly. This harness should incorporate the latest technologies in corrosion and contamination prevention. In addition, a harness should be designed to be modular in nature, allowing the troubleshooting and replacement of only those sub-assemblies that had failed without the disruption of the rest of the systems and cancellation of flights. Since a harness of this kind would be modular in nature, then only those sub-assemblies would need to be maintained in inventory, vastly reducing the cost associated with operating this harness.